1. Field of the Invention
The present invention relates to a flange connection for fiber-reinforced plastic pipe pieces which are composed of an inner layer of thermoplastic material and an outer layer of wound fiber impregnated with synthetic resin.
2. Description of the Prior Art
For conducting media, particularly aggressive media in the chemical industry, pipes are used which are composed of an inner layer of a thermoplastic material, such as, polyethylene, polypropylene, polyvinylchloride, etc., and of an outer layer of a fiber-reinforced laminate, such as, wound glass fibers impregnated with an unsaturated polyester resin or epoxy resin. The outer laminated layer has the purpose to reinforce the pipes, so that media can be conducted at high pressures. The outer laminated layer also serves to absorb external forces which act on the pipe, such as, tension/compressive forces or bending forces.
When preparing detachable connections between pipes or between pipes and fittings, such as, angles, tees, or reducing pieces, it is important that the medium not come into contact with the outer layer and that the external forces are essentially transmitted through the outer layer.
In a known flange connection according to German Industrial Standard DIN 16966, Type B, the facing surfaces of the end of the pipe and of a flanged sleeve are conically inclined and the surfaces are glued together. This results in a glued connection, however, the parts are not connected to one another in a locking manner. The resulting connection between flanged collar and outer layer of the pipe is of insufficient strength.
In another known flange connection of the afore-described type, see EP-A2-152753, the flanged collar is fastened to a tubular part by means of a thread. However, it is difficult to make threads on parts which are made of glass fiber laminates and the quality of the thread is frequently not satisfactory for a trouble-free connection. In addition, free space is required for screwing the flanged sleeve in axial direction, this free space frequently not being available at the location where the connection is to be made.
Therefore, it is the primary object of the present invention to provide a flange connection of the above-described type, in which the above-described disadvantages are avoided, which can be made at the location where the connection is to be used, and which meets the above-mentioned requirements with respect to the transmission of forces and the surfaces with which the medium to be conducted comes into contact.